SERVICING
13
Test for continuity using a VOM and if not as above,
replace the control.
Checking High Pressure Control
WARNING
High Voltage!
Disconnect all power before servicing or
installing. Multiple power sources may be present.
Failure to do so may cause property damage,
personal injury or death.
The high pressure control capillary senses the pressure in
the liquid or discharge line. If abnormally high condensing
pressures develop, the contacts of the control open,
breaking the control circuit before the compressor motor
overloads. This control is automatically reset.
1. Using an ohmmeter, check across terminals of
high pressure control, with wire removed. If not
continuous, the contacts are open.
2. Attach a gauge to the dill valve port on the base
valve.
With power ON:
WARNING
Line voltage now present.
3. Start the system and place a piece of cardboard in
front of the condenser coil, raising the condensing
pressure.
4. Check pressure at which the high pressure control
cuts-out.
If it cuts-out at 660 PSIG ± 10 PSIG, it is operating normally
(See causes for high head pressure in Service Problem
Analysis Guide). If it cuts out below this pressure range,
replace the control. The control should reset at 420 PSIG +
25 PSIG.
Checking Capacitor
Capacitor, Run
A run capacitor is wired across the auxiliary and main
windings of a single phase permanent split capacitor
motor. The capacitors primary function is to reduce the line
current while greatly improving the torque characteristics
of a motor. This is accomplished by using the 90° phase
relationship between the capacitor current and voltage
in conjunction with the motor windings so that the motor
will give two phase operation when connected to a single
phase circuit. The capacitor also reduces the line current to
the motor by improving the power factor.
Capacitor, Start
Scroll Compressor Models
Hard start components are not required on Scroll
compressor equipped units due to a non-replaceable check
valve located in the discharge line of the compressor.
However hard start kits are available and may improve low
voltage starting characteristics.
This check valve closes off high side pressure to the
compressor after shut down allowing equalization through
the scroll flanks. Equalization requires only about one or
two seconds during which time the compressor may turn
backwards.
Your unit comes with a 180-second anti-short cycle
to prevent the compressor from starting and running
backwards.
Models Equipped With A Hard Start Device
A start capacitor is wired in parallel with the run capacitor
to increase the starting torque. The start capacitor is of the
electrolytic type, rather than metallized polypropylene as
used in the run capacitor.
A switching device must be wired in series with the
capacitor to remove it from the electrical circuit after the
compressor starts to run. Not removing the start capacitor
will overheat the capacitor and burn out the compressor
windings.
These capacitors have a 15,000 ohm, 2 watt resistor
wired across its terminals. The object of the resistor
is to discharge the capacitor under certain operating
conditions, rather than having it discharge across the
closing of the contacts within the switching device such as
the Start Relay, and to reduce the chance of shock to the
servicer. See the Servicing Section for specific information
concerning capacitors.
Relay, Start
A potential or voltage type relay is used to take the start
capacitor out of the circuit once the motor comes up to
speed. This type of relay is position sensitive. The normally
closed contacts are wired in series with the start capacitor
and the relay holding coil is wired parallel with the start
winding. As the motor starts and comes up to speed, the
increase in voltage across the start winding will energize
the start relay holding coil and open the contacts to the
start capacitor.
Two quick ways to test a capacitor are a resistance and a
capacitance check.
